1. Field of the Invention
The field of the present invention is internal combustion engines of a type having a fuel injection valve provided with assist air supply means for finely atomizing fuel and disposed in an intermediate portion of an intake passage, and with swirl control means for producing a swirl in the combustion chamber in accordance with certain operational conditions of the engine, which engine is capable of conducting a lean burn.
2. Description of the Prior Art
There is a conventionally known engine in which the amount of the assist air is control led in accordance with the operational condition of the engine as described, for example in Japanese Utility Model Application Laid-Open No. 76558/89.
In such a prior art engine, when the air assisting is carried out in the condition where the swirl is produced in the combustion chamber in order to promote the lean burn, the assisting air hinders the production of the swirl and the lean burn cannot be achieved sufficiently. Also, in a non-swirl operational region in which the engine temperature is low, it is difficult to finely atomize the fuel since the intake air is reduced in velocity in the intake passage. For this reason, the fuel is likely to cling to an inner wall of the intake passage, leading to a deterioration in driveability. In such a case, if the air assisting is carried out, the fine atomization of the fuel will be promoted. Moreover, the limit of lean burn varies in accordance with the temperature of the engine. Accordingly, it has been found by the inventors that it is advantageous for the air assisting to be carried out in response to the temperature of the engine, the range of the swirl operation and the range of the lean burn, in order to obtain a suitable operation of the engine.